Did climate change create a mysterious civilization 5,000 years ago?

The ancient Peruvians probably used simple irrigation systems like those seen today in Supe Valley.

AP Photo/Jonathan Haas, Field Museum

­When a team of archaeologists found dozens of huge mounds buried in the arid valleys of Norte Chico, questions started flying.

Not only were archaeologists unable to attribute the mounds to any previously known South American civilizations, there were no other remnants typically associated with an architecturally sophisticated civilization. This is perhaps why this mysterious civilization escaped attention for so long.

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But they did find something that opened up a whole new can of worms: seashells and fish bones.

What are the remains of sea life doing in a desert landscape? One likely answer offers a theory of the origins of the mound builder civilization 5,000 years ago: The mound builders were fishermen who had to move inland when their livelihood was threatened by climate change.

The archaeologists who made the discovery are still working to prove the climate-change theory, analyzing the rings in the seashells to get evidence of changing ocean temperatures. The theory goes like this:

Five-thousand years ago, fisherman thrived along the coastline of Peru, about 10 miles (16 kilometers) from the Norte Chico region. They were hunter-gatherers who survived by using sea resources. But suddenly, around 3000 B.C., something changed [source: Joyce]. A climate shift, a change in the interaction between the atmosphere and the water, threatened the viability of their fishing lifestyle.

The change would have come in the form of more frequent El Niño weather systems. El Niño is the regular climate phenomenon that brings heavy rains and warmer ocean temperatures to South America. It's a normal, cyclical occurrence related to the timing and duration of hurricane season. It affects flooding, temperature and sea life, and it occurs perhaps once every few years depending on location. A sudden increase in frequency could have drastic consequences for coastal dwellers. Ocean temperatures warm up, altering the distribution of sea life, and endless torrential rains lead to flooding.

So the fishermen moved inland. They abandoned their hunter-gatherer lifestyle and had to come up with a new food source. What we see now as a desolate landscape would have been fertile as a result of that climate change. With so much water suddenly available, irrigation became a relatively simple solution. They turned to agriculture, cultivating crops. They traded these crops with people who stayed on the coast and kept fishing -- thus the fish bones and shells scattered throughout the region.

This type of centralized, communal food production and organized trade for resources would have led to a centralized society. They built permanent homes and sunken plazas for gathering. The mound builders seem to have had an organized government and religion.

The civilization lasted for about a millennium [source: ScienceDaily]. Geological discoveries point to an end very similar to the beginning: Another shift in climate made irrigation more difficult, and the mound builders moved away to more fertile ground, leaving behind their world.

­With the entire globe facing the prospect of climate change, the discovery of the mound builder civilization may be a telling one. It's not the first society believed to have been monumentally affected by weather shifts. The fall of the Tang Dynasty in ­China in 907 A.D. is linked to a climate shift that altered China's monsoon season and led to severe, extended drought. Around that same time, the Mayan civilization collapsed due to a series of droughts that diminished the water supply. The common link, aside from drought, appears to be a resistance to change. It's a logical end: An agriculture-based society collapses in the face of water shortage. A society that shifts with the weather -- perhaps moving from agriculture-derived resources to trade-based ones -- has a better chance of surviving a climate shift that threatens its way of life.